1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to an image sensor having an improved resolution and an image sensing method using the same. More particularly, apparatuses and methods consistent with the present invention relate to an image sensor capable of improving the resolution of images without modifying the resolution of a photoelectric conversion semiconductor device for sensing images and an image sensing method using the same.
2. Description of the Related Art
As generally known in the art, image sensors convert one-dimensional or at least two-dimensional optical information into electric signals. Image sensors are classified into image sensing tubes and solid-state image sensing devices. The image sensing tubes have been widely used for measurement, control, recognition, etc. based on image processing technology in the television industry and applied techniques have been developed accordingly. The solid-state image sensing devices are made of photoelectric conversion semiconductors to convert optical images into electric signals. The solid-state image sensing devices are classified into Metal Oxide Semiconductor-type MOS devices and Charge Coupled Device-type (CCD) devices.
Complimentary Metal Oxide Semiconductor (CMOS) image sensors convert optical images into electric signals by using CMOS semiconductor technology. Particularly, MOS transistors are fabricated as much as pixels and are used to detect output successively (i.e., switch mode). Compared with conventional CCD image sensors, CMOS image sensors are convenient to drive and enable various scanning modes. In addition, they have the advantage of compactness, because signal processing circuits can be integrated into a single chip.
Recently, various multimedia appliances (e.g., mobile telephones, PDAs) are equipped with devices for sensing or displaying images. For example, compact camera modules are used as image input devices. As consumers increasingly demand high-quality images, many efforts have been made to improve the resolution of image sensors used as image input devices.
FIG. 1 is a perspective view showing a conventional image sensor adapted to sense images through photoelectric conversion.
Referring to FIG. 1, the conventional image sensor includes a photoelectric conversion semiconductor device 10, a color filter array 20, and a micro-lens array 30.
The photoelectric conversion semiconductor device 10 is fixedly mounted on top of a scanner and has a number of pixels arranged on the front surface so as to constitute a light receiving unit. Particularly, each pixel generates a signal charge in proportion to the intensity of light incident on the pixel.
The color filter array 20 is adapted to create color digital images and has an array of filters (e.g., red, green, and blue filters), which correspond to the pixels of the photoelectric conversion semiconductor device 10 on a one-to-one basis. The color filter array 20 is formed on top of the light receiving unit of the photoelectric conversion semiconductor device 10 through a lithography process, for example.
The micro-lens array 30 consists of a number of lenses, e.g. hemispherical micro-lenses 31, which are two-dimensionally arranged on top of the color filter array 20. The lenses are aligned with respective pixels of the photoelectric conversion semiconductor device 10 (as in the case of the filters of the color filter array 20) so as to increase the amount of light incident on the light receiving unit.
In order to improve the resolution of the conventional image sensor, which is constructed as mentioned above, the pixels of the photoelectric conversion semiconductor device 10 must be increased.
FIG. 2 shows a method for increasing the number of pixels of a photoelectric conversion semiconductor device of a conventional image sensor, in order to improve the resolution.
Referring to FIG. 2, the number of pixels 11 of the photoelectric conversion semiconductor device 10 can be increased either by increasing the size of the photoelectric conversion semiconductor device 10 itself or by reducing the size of respective pixels 11.
If the number of pixels is increased while maintaining their size, the chip size of the photoelectric conversion semiconductor device 10 is increased in proportion. This costs more money. Furthermore, the increase in chip size reduces the yield rate, which further increases the cost.
If the number of pixels is increased while maintaining the chip size of the photoelectric conversion semiconductor device 10, the size of the pixels 11 becomes smaller. This makes the manufacturing process difficult. In addition, since the sensitivity of the pixels is degraded, they are more affected by noise and exhibit poorer performance. Therefore, this approach is impractical.